If one takes into account the many constraints (cost, post office approval, customer requirements, mechanical requirements, human readability) that must be simultaneously satisified, it may fairly be said that it is not easy to print postage. For nearly a hundred years, companies such as Hasler (a predecessor of the assignee of the present invention) and its competitors have provided postage meters which print postage by means of mechanical relief die plates. Generations of mechanical engineers have developed and refined the art of mechanical printing of postage so that today's postage meters (also called franking machines) offer a high-quality die-printed postage indicium together with the all the benefits flowing from the use of microprocessors.
It has been recently suggested to use digitally formed indicia instead of die-printed indicia, a move which would discard a substantial fraction of the accumulated experience with die printing of postage and which opens up a host of new problems. The printing technologies most often proposed for digitally formed indicia are ink-jet and laser printing. These technologies have many potential disadvantages. Among them is that if the postal indicia are to be printed with an off-the-shelf printer connected to a postal security device via a nonsecure data link, then encrypted information must be printed within the indicia to assist in distinguishing between authentic and fraudulent indicia. The encrypted information is generated by cryptographic apparatus within the postal security device.
It is considered desirable, and is known in the art, to provide time and date information as inputs to the cryptographic apparatus within the postal security device (PSD or client). The encrypted information from the PSD is applied to a mail piece in the postal indicia. Such information is more helpful to the post office for authentication purposes than an indicium that lacks any encrypted information containing time/date information.
At least one postal authority has suggested that it is preferable to have, within the postal security device, a time base that is powered by a reliable power supply that is provided without interruption even when AC (mains) power is removed. With such a device, even when the power is turned off or disconnected by a user (or is lost due to a utility power outage) the time base or real-time clock is continuously running, consuming power from the internal reliable power supply.
For the internal time base to be of any meaningful help for authentication purposes, it must be quite accurate, typically requiring an accuracy better than that of a consumer wristwatch. Such a time base generally relies upon a crystal oscillator, and the crystal for this purpose is more expensive than the inexpensive crystal used in a consumer wristwatch. The high-accuracy time base and internal reliable power supply all add to the cost of the postal security device.
Such a system generally relies on the internal power source working without interruption, and in the event of loss of the internal power source, a variety of manual steps are generally required to restore normal function, steps including taking the postal security device out of service. Such steps are at best annoying to the user, and may be very disruptive for the user.
It would be desirable to reduce the cost of the postal security device, to make it less likely to require being taken out of service, and yet to maintain the authentication benefits that come from the use of a consistent time base that matches the rest of the system.